[PATCH v3 10/13] mm/huge_memory: separate out the folio part of zap_huge_pmd()

Lorenzo Stoakes (Oracle)
2026-03-20T18:08:03Z

Place the part of the logic that manipulates counters and possibly updates
the accessed bit of the folio into its own function to make zap_huge_pmd()
more readable.

Also rename flush_needed to is_present as we only require a flush for
present entries.

Additionally add comments as to why we're doing what we're doing with
respect to softleaf entries.

This also lays the ground for further refactoring.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
mm/huge_memory.c | 61 +++++++++++++++++++++++++++---------------------
1 file changed, 35 insertions(+), 26 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 673d0c4734ad..9ddf38d68406 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2325,6 +2325,37 @@ static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
mm_dec_nr_ptes(mm);
}

+static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma,
+ pmd_t pmdval, struct folio *folio, bool is_present,
+ bool *has_deposit)
+{
+ const bool is_device_private = folio_is_device_private(folio);
+
+ /* Present and device private folios are rmappable. */
+ if (is_present || is_device_private)
+ folio_remove_rmap_pmd(folio, &folio->page, vma);
+
+ if (folio_test_anon(folio)) {
+ *has_deposit = true;
+ add_mm_counter(mm, MM_ANONPAGES, -HPAGE_PMD_NR);
+ } else {
+ add_mm_counter(mm, mm_counter_file(folio),
+ -HPAGE_PMD_NR);
+
+ /*
+ * Use flush_needed to indicate whether the PMD entry
+ * is present, instead of checking pmd_present() again.
+ */
+ if (is_present && pmd_young(pmdval) &&
+ likely(vma_has_recency(vma)))
+ folio_mark_accessed(folio);
+ }
+
+ /* Device private folios are pinned. */
+ if (is_device_private)
+ folio_put(folio);
+}
+
/**
* zap_huge_pmd - Zap a huge THP which is of PMD size.
* @tlb: The MMU gather TLB state associated with the operation.
@@ -2340,7 +2371,7 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
bool has_deposit = arch_needs_pgtable_deposit();
struct mm_struct *mm = tlb->mm;
struct folio *folio = NULL;
- bool flush_needed = false;
+ bool is_present = false;
spinlock_t *ptl;
pmd_t orig_pmd;

@@ -2369,14 +2400,11 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,

if (pmd_present(orig_pmd)) {
folio = pmd_folio(orig_pmd);
-
- flush_needed = true;
- folio_remove_rmap_pmd(folio, &folio->page, vma);
+ is_present = true;
} else if (pmd_is_valid_softleaf(orig_pmd)) {
const softleaf_t entry = softleaf_from_pmd(orig_pmd);

folio = softleaf_to_folio(entry);
-
if (!thp_migration_supported())
WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
} else {
@@ -2384,33 +2412,14 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
goto out;
}

- if (folio_test_anon(folio)) {
- has_deposit = true;
- add_mm_counter(mm, MM_ANONPAGES, -HPAGE_PMD_NR);
- } else {
- add_mm_counter(mm, mm_counter_file(folio),
- -HPAGE_PMD_NR);
-
- /*
- * Use flush_needed to indicate whether the PMD entry
- * is present, instead of checking pmd_present() again.
- */
- if (flush_needed && pmd_young(orig_pmd) &&
- likely(vma_has_recency(vma)))
- folio_mark_accessed(folio);
- }
-
- if (folio_is_device_private(folio)) {
- folio_remove_rmap_pmd(folio, &folio->page, vma);
- folio_put(folio);
- }
+ zap_huge_pmd_folio(mm, vma, orig_pmd, folio, is_present, &has_deposit);

out:
if (has_deposit)
zap_deposited_table(mm, pmd);

spin_unlock(ptl);
- if (flush_needed)
+ if (is_present)
tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
return true;
}
--
2.53.0